Properties of substituted 2-trifluoromethylbenzimidazoles as uncouplers of oxidative phosphorylation

Abstract

1. The activity of 25 substituted 2-trifluoromethylbenzimidazoles in uncoupling oxidative phosphorylation by rat-liver mitochondria has been compared. 2. For halogen- or mixed-halogen- and alkyl-substituted analogues, uncoupling activity was proportional to the acidity of the imidazole -NH group. Tetrachloro-2-trifluoromethylbenzimidazole was the most active (50% uncoupling of oxidative phosphorylation at 7.9x10(-8)m, pK5.04). Nitro-substituted analogues were less active than predicted from pK considerations or from partition-coefficient measurements. 3. Introduction of an -NH(2) or -CO(2)H substitutent caused a loss of uncoupling activity, as did alkylation at position 1 of the imidazole ring. 4. Benzimidazoles active as uncouplers stimulated mitochondrial adenosine triphosphatase but not all stimulated the oxidation of succinate in the absence of a phosphate acceptor. 5. 4,5-Dichloro-2-trifluoromethylbenzimidazole inhibited the succinate-oxidase system at about the same concentration required for uncoupling (0.52mum for 50% inhibition of both activities) and the site of this inhibition appears to lie between succinate dehydrogenase and cytochrome b.

Mitochondrial Targets of Drug Toxicity

“…The most efficient uncoupler of this class is S-13, 2',-5-dichloro-4'-nitro-3-tert-butyl-salicylanilide, which induces complete uncoupling at only 0.2 molecule per cytochrome oxidase heme aa3 (which is about 42 pmol of uncoupler per mg of mitochondrial protein). The mechanism of the uncoupling action is similar to that of other A ‫מ‬ protonophores (129). Structure-activity relationships with 28 derivatives substituted at both the salicylic acid moiety and the aniline moiety revealed that both hydrophobicity and electron-withdrawing power were necessary for uncoupling activity (130).…”

“…The most active uncoupler of this class is 4,5,6,7tetrachloro-2-trifluoromethylbenzimidazole (TTFB), which produces 50% uncoupling of oxidative phosphorylation (measured as ATP synthesis) at 8 x 10 ‫8מ‬ M in isolated liver mitochondria (127) (compared with 8 ‫ן‬ 10 ‫6מ‬ M for DNP under the same experimental conditions). Similar to other acidic uncouplers, the efficiency of TFB derivatives increases with the acidity of the dissociable -NH-group (128,129).…”

Development of a Decision Tree for Mitochondrial Dysfunction: Uncoupling of Oxidative Phosphorylation

“…all rings can be substituted or part of a larger structure, R and n denote the substituent or chain length used to calculate the shown p K a value. Alert names are as detailed in the original literature sources …”

Predicting Uncoupling Toxicity of Organic Acids Based on Their Molecular Structure Using a Biophysical Model

“…Because of these reversed gradients as compared to mitochondria, they are less sensitive to the limiting effects of the neutral permeability. Isolated mitochondria ,,,,,− are a very direct test system for measuring uncoupling activity because in the absence of inhibiting effects, the change in respiration rate is a direct indicator for uncoupling activity. Additionally, intact algae cells ,, were included to show the impact of the ion-trapping effect on uncoupling activity, which can lead to a pH-dependence of uncoupling.…”